Light beams or optical signals are frequently used to transmit digital data. For example, optical signals can be used to transmit data between electronic components on a single circuit board, or between electronic components on nearby circuit boards. Increasingly, optical signals are being used to transmit data between sub-components within integrated circuits.
Optical signals can be routed using waveguides. Waveguides carry optical energy by imposing boundaries which control the expansion of the optical energy and guide it to a desired location. Optical waveguides are typically constructed of a dielectric material with a relatively high index of refraction which is surrounded by a material with a lower permittivity such as cladding or air. For example, ridge waveguides can be constructed to carry optical signals between sub-components within an integrated circuit. Typically, a ridge waveguide is an elongated structure with a rectangular or circular cross-section that optically connects a signal source to one or more detectors. The ridge waveguide can be made from a variety of materials that are at least partially transparent at a target optical wavelength or range of wavelengths.
The design and manufacture of integrated optical circuits is made much more complicated when waveguides have to cross each other. One possible approach to this issue is to route one of the crossing waveguides out of the plane of the circuit to pass over or under the other waveguide. However, adding such out-of-plane structure to the manufacture of the integrated optical circuit greatly increases the complexity and cost of manufacturing the integrated optical circuit. Additionally, turns or curves in the waveguide out of and back into the circuit plane may result in unwanted reflection or loss or signal strength.
Throughout the drawings, identical reference numbers designate similar, but not necessarily identical, elements.